As people pay attention to green energy saving and product intelligence, ambient light sensors are applied more and more widely. An ambient light sensor can measure and capture illumination intensity of current ambient light, and can adjust luminance of various light emitting elements automatically according to the illumination intensity, optimize luminance control, and reduce power consumption of products. Common light emitting elements include a display screen, a keyboard backlight, and so on. For example, in mobile applications such as mobile phones, electricity consumed by a display is up to 30% of the total capacity of the battery. An ambient light sensor can detect the brightness and darkness of the environment, and the mobile phone may reduce luminance of the display in a relatively dark environment to reduce power consumption and prolong the service time of the battery as much as possible.
An ambient light sensor needs to convert received optical signals into electrical signals so as to implement the functions of a light sensor. Therefore, a terminal device needs to provide a photosensitive zone for the ambient light sensor. For example, by forming a hole on the terminal device or other means, light can be irradiated to the ambient light sensor. However, to show characteristics such as portability, some terminal devices nowadays become increasingly smaller and thinner. In this case, it is necessary to utilize every tiny space. Therefore, the ambient light sensor is relatively simple, and the photosensitive zone provided on the terminal device for it is very small, which, however, will bring adverse effects. For example, for a mobile phone, the effective exposure area of the ambient light sensor is generally a few tenths of a millimeter. In such conditions, if the mobile phone has dust that just covers the effective exposure area of the ambient light sensor due to improper sealing, or a fingerprint of the user just covers the effective exposure area of the ambient light sensor, the amount of incident ambient light may be affected, so that the amount of the ambient light actually irradiated onto the effective exposure area of the ambient light sensor may be greatly reduced, which leads to an increased recognition error, and may further affect the effectiveness of the terminal device in controlling light emitting elements (including the display screen, the keyboard backlight, and so on).